1. Field of The Invention
The present invention relates generally to an apparatus for controlling a damping coefficient of a shock absorber (also called a damper, but hereinafter referred to as the shock absorber) interposed between an unsprung mass and sprung mass of the vehicle so as to provide an optimum damping force therefrom. The shock absorber is provided with changing means for changing the damping coefficient thereof at multiple stages in response to a control signal.
2. Description of The Background Art
A Japanese Utility Model Registration Application First Publication No. Showa 61-127007 published on Aug. 9, 1986 exemplifies a previously proposed apparatus for controlling a damping coefficient of the shock absorber.
The previously proposed damping coefficient controlling apparatus includes: a sprung mass displacement measurer; a relative speed measurer between the unsprung mass and the sprung mass; and a control signal output generator.
The control signal output generator outputs a control signal so as to provide a low damping coefficient for the shock absorber when a sign of a direction of the sprung mass displacement coincides with that of the direction of the relative speed and outputs the control signal so as to provide a high damping coefficient for the shock absorber when the sign of the direction of the sprung mass displacement does not coincide with that of the direction of the relative speed.
To pick up a frequency required to control the damping coefficient, waveforms appearing on the signals derived from the sprung mass displacement measurer and from the relative speed measurer are processed using the low-pass filter and high-pass filter circuits.
On the other hand, if the vehicle speed is changed, a frequency characteristic of the detection signal of the sprung mass longitudinal speed is accordingly varied. Since a frequency band to pass through the filter circuits of the previously proposed damping coefficient is fixed, such signals required to control may not be detected and input to a controller and control lag and/or advance may occur.
If a filtered frequency band of each filter is set over a wider frequency band, such a frequency band as not to be required to control may be detected and input, a favorable control effect may not be achieved.